Polycyclic aromatic polymer as a photoconductor or overlayer

ABSTRACT

A polyvinylpyrenal copolymer obtained by condensing the corresponding aromatic aldehyde with a copolymer of vinyl alcohol and having a number average molecular weight of at least 5,000. Also included are photoconductive members utilizing such material as an intrinsic photoconductor or as matrix material, demonstrating excellent structural and electronic properties for xerographic purposes.

[ill 3,884,689

[ May 20, 1975 POLYCYCLIC AROMATIC POLYMER AS A PHOTOCONDUCTOR OR OVERLAYER [75] Inventor: William W. Limburg, Peniield, N.Y.

[73] Assignee: Xerox Corporation, Stamford.

Conn.

[22] Filed: Aug. 30. 1973 [2!] App]. No.: 393,082

[52] U.S. Cl 96/l.5; 260/73 R; 96/i.8 [5i i int. Cl G03g 5/06 [58] Field of Search 96/i.5, 1.8; 260/73 R [56] References Cited UNITED STATES PATENTS 3.113.022 12/1963 Cassiers et al. 96/i.5 3.102.532 l2/i9b4 Hoegl el al. 96/|.5 3.l63.53l l2/i964 Schlesinger 96/i.5 3.240.597 3/l966 Fox 96/l.5 3.307.940 3/i967 Hoegl et al. 96/i.5 X

3.373.14l 3/1968 At'tergut 96/i.5 X 3,459.69! 8/ I969 Ostrowski et al. 260/73 R )t 3.$l4.435 5/1970 Ardis et al. 260/73 R )t 3.655.378 4/1972 Contois et al Jo/L5 3,740.2]8 6/l973 Contois ct al 96/ I .5 3.765.884 l0/l973 Shea Jo/L5 X Primary Examiner-Roland E. Martin. Jr. Attorney. Agent. or Firm-John E. Crowe'. James P. O'Suliivnn; James J. Ralabate [57] ABSTRACT A polyvinylpyrenal copolymer obtained by condensing the corresponding aromatic aldehyde with a copoly mer of vinyl alcohol and having a number average mo lecular weight of at least 5,000. Also included an photoconductive members utilizing such material a: an intrinsic photoconductor or as matrix material demonstrating excellent structural and electroni properties for xerographic purposes.

14 Claims, No Drawings I POLYCYCLIC AROMATIC POLYMER AS A PHOTOCONDUCTOR OR OVERLAYER BACKGROUND OF THE INVENTION In the electrophotographic or xcrographic art it is customary to utilize photoreceptor plates having at least an external photoconductive insulating layer and a charge conductive supporting substrate. Generally. a photoconductive layer is uniformly elcctrostatically charged in the absence of light or other activating radiation and. thereafter. exposed to a light pattern which can correspond to a negative image. The areas of the photoconductive layer which are so exposed selectively lose their charge much more rapidly than non-exposed areas. As a result. the photoconductive layer at least temporarily retains a charge corresponding essentially to a latent positive image. This image can then be conveniently developed to form a visible positive image by contacting with oppositely charged pigmented particles. commonly identified as toner particles. which will adhere mostly to the charged areas. The resulting image may optionally be permanently affixed to the photoconductor if the imaging layer is not to be reused. This usually occurs with binder-type photoconductive films where the photoconductive imaging layer is also an integral part of the finished copy.

Where plain paper" copying systems are involved, however. the latent image is conveniently developed on the imaging surface of a reusable photoconductor. or transferred to another surface such as a sheet of paper. and thereafter developed. After a latent image is developed on the imaging surface of a reusable-type photoconductor. it is transferred to another substratc.and then permanently affixed by using any one of a variety of well-known techniques such as by overcoating with a transparent film. or by thermal fusion of the toner particles to the sheet. In such a copying system the materials in the photoconductive layer must be capable of rapidly changing from an insulative, to a chargeconductive. and then back to an insulative condition to permit cyclic use of the imaging surface. Failure to revert back to the insulative state before each succeeding charging sequence will result in a high dark decay rate commonly referred to as fatigue." In the past. the problem has been controlled. to some extent. simply by selection of those photoconductive materials having the best known rapid switching capacity. Typical of such materials are anthracene. poly(N-vinylcarbazole). sulfur, selenium. selenium alloys. metal-free phthalocyanines. etc.. and mixtures thereof (U.S. Pat. No. 2.297.691

While organic photoconductive materials such as poly(N-vinylcarbazole) generally have good dark decay characteristics. they generally lack sufficient inherent photosensitivity to be completely competitive with selenium. For this reason. they are usually used together with activators." Poly(vinylcarbazoles). for example, are sensitized with 2.4.7-trinitro-9-fluorenone to obtain improved photorcsponsc. discharge characteristics. and even some improvement in dark decay characteristics (ref. U.S. Pat. No. 3.484.237). There are also other organic resins which are traditionally considered non photoconductive. but which can be sensitized with Lewis Acids to form charge-transfer complexes which are photoresponsive at the visible end of the spectrum. U.S. Pat. Nos. 3.408.181; 3.408.182; 3.408.183; 3.408.184; 3.408.185. 3.408.186; 3.408.187; 3.408.188; 3.408.189; and 3.408.190 are of interest in this area.

2 For all practical purposes. the amount of sensitiza tion of both photoconductive and non photoconductive resins depends upon the concentra tion of the activator; within limits. the higher ,the load 5 ing. the greater the photoresponse obtained. Unfortu natcly. however. loadings exceeding about weigh percent of the photoconductive composition will usu ally impair mechanical and/or photoconductive prop erties of the sensitized composition. Excessive amount: it) of activator in either a photoconductive or a nonphoto conductive material of the type disclosed in the fibOVt patents will tend to crystallize out of the photoconduc tive composition.

The above inherent limitations make it very difficul l5 and often times impossible to obtain the much-desiret marriage ofa high quantum efficiency photoconducto with a tough. transparent. flexible, active matrix mate rial having a low injection threshold.

One very useful discovery in this area utilizes variou protective polymeric overcoats capable of holding charge of high field strength on an external surface an also permitting selective transmittal of carriers from photoconductive layer through the polymeric overcoa None of the known active matrix materials. howevei are capable of satisfying all of the important physicz and electronic properties needed for modern xerc graphic or electrophotographic usage.

OBJECTS OF THE INVENTION It is an object of the present invention to obtain a ne class of polymeric materials having the necessary phys cal and electrical properties to permit a wider and mor flexible use of xerographic principles for copying pui poses.

It is a further object to synthesize and utilize a ne class of intrinsic organic photoconductors which can b combined with a substantial functional amount of a activator without unduly affecting its mechanical c photoconductive properties.

A further object of the present invention is to di; cover and synthesize a new active polymeric materi: which is compatible with high quantum efficiency ph( toconductor material and which retains its flexabilit and durability.

SUMMARY OF THE INVENTION These and other objects are realized by the disco ery, preparation and utilization of a new class of an matic polyvinyl polymers and elements utilizing suc polymeric material conveniently represented by t1 formula:

CM- CH CH CH l OH l sl or defined as a N- or S-containing heterocyclic group, including a 3 ringed N-containing heterocyclic group of the formula in which R, and R, are individually defined at each occurrence as a lower alkyl group of l-8 carbon atoms; a lower alkoxy of 1-8 carbon atoms, a halo group such as chloro and bromo an amino group including N, N, disubstituted lower alkyl amino groups, and a cyano group, such groups being preferably attached to one or more of the aromatic rings of the ring systems of formula (ID-(1V); R is a lower alkyl exemplified as an alkyl of 1-8 carbons such as octyl; q is defined as -2 and preferably 0-1.

R of formula I is defined as a polymeric end group including the residue of an initiating chain or otherwise defined as a hydroxyl or ester group such as an alkyl carbonyl or an aryl carbonyl group in which the alkyl moiety usefully contains 1-18 carbon atoms and the aryl moiety is a phenyl group such as phenyl, hydroxy phenyl, an alkyl phenyl or a halo phenyl group:

R, is defined as a hydrogen atom, a lower alkyl group,

including alkyl groups of 1-8 carbon atoms such as methyl, propyl, isopropyl and n-octyl, and preferably as an acyl group such as a lower alkyl carbonyl including R, is a polymeric end group, including hydrogen or an acyl group such as an alkyl carbonyl having an alkyl moiety of l-l8 carbon atoms and an aryl carbonyl such as a phenyl carbonyl exemplified by phenylcarbonyl, alkyl substituted phenylcarbonyl or halophenylcarbonyl', and

m, n, 0 and p are positive number commensurate with a number average molecular weight of at least about 5,000, conveniently varying from about 5,000 300,000 or higher and preferably greater than about 10,000; m, n and 0 falling within the respective ratios of about l-6:0l:18 in random or block polymers, and p being defined commensurate with the above molecular weights. For purposes of the present invention a preferred, although non-exclusive number average molecular weight extends from 10,000 to 300,000 depending upon the ratio of monomeric units and the definitions of R, and R,. The preferred ratio of m:n:0 is about 3-6:0-l:l-8.

Suitable monomeric components and ratios thereof which are includible within the present invention are set forth in Table 1 below with respect to formula 1.

(I) T c if cHcH 2 14/0 m '2 cg- -cn CH CH OH L o TABQE I Approximate Number Average KW R1 R2 R3 R4 R5 R6 Ratio manzo 2-1- 12 000 ca -coon a a -oca 5m:

P-2 10,000 CH3- CH3- 620:1

0-: V 10.000 cu -cou u um 9-5 250,000 c n- 4=1=a P-6 1,000,000 H (ca u- 3=h8 P-7 11,000 ca -co- O? OH H -0ca 6:1:6 00 R, 6 15,000. -OCHJ 320: 20,000 w n 3-110 n P-IO 50,0 H 3:0:

30 Polymers or terpolymerswithin the scope ofthe presin accordance with the following general reac ent invention can be conveniently synthesized, for inmechanism, in which the radicals are defined as in stance, by reacting carboxyaldehyde of the desired mulae I-lV supra:

CH ---CH2 C H CH OR sum ,CH2 CH col-0H Qg m CH "CH CH- 2 I 2 OH on,

polycyclic group with a homopolymer or a copolymer The desired product can also include, for inst 3,884,689 7 8 the reaction ol'a completely hydrolyzed poly(vinylacetained from commercial sources, the aldehyde reactate) in accordance with the following formulae: tants being synthesized, for instance. by reacting pure ulcn l The above reaction best proceeds in asolvent having pyrene with POCh, N-methyl fomtanilide and oa high hydrogen bonding capability such as alcohols dichlorobenzene in accordance with the Vilsmeier reand water, dimethyl sulfoxide, or hexamethylphosaction. ph0l'3mid8. Bulletin of the Chemical Society of Japan, Vol. 41, 2719-22, 1968.

Preformed polymeric reactants such as the poly(- Synthesis of various aldehyde precursors can be efvinylalcohol) of formula N can be conveniently obfected as follows wherein R, is defined as above:

[H] A. R2 1121802 P4. H R2 NHZ R2 N(CH3)2 utcn t o-dichloro benzene 13. R 1: 2oc1 -C12 a cao [H] R2-CH3 CHO "ll-e1 1 oc1 cu Vilsmeier Reaction (see page 9) ChemicaI Abstracts v01. 50. 1200a memical Abstracts, Vol. 56, 1407-1408 The following Examples further illustrate certain preferred embodiments of the invention.

EXAMPLE I (P-3) .0l2 Mole of l-pyrenecarboxyaldehyde obtained by the Vilsmcier reactionis slowly added, with agitation, to a vinylacetate/vinylalcohol copolymer l:6) containing .012 molar equivalents of (-OH) functional groups in dimethyl sulfoxide. The reaction is allowed to proceed in the presence of about .25 gm. of toluene sul l'onic acid for about 4 hours at about I lOC.. and the resulting terpolymer product is recovered by precipitation from cold acetone. The product is found soluble in THF and CHCl- CHCb. and conveniently cast from a "lHF-Tetrachloroethane solution to obtain a clear. hard. tough flexible film. The product, identified as P-3. is tested and reported in Tables l-lll, and exhibits the following characteristics:

UV: x max 328,343 nm Solubility: THF,CHCl CHCl Analysis pyrene by weight) 58.l%

EXAMPLE ll (P-2) .l2 Mole of 6, 9-dimethyl-pyrene-l carboxaldehyde obtained by the Vilsmcier reaction is admixed with at least 99% hydrolyzed poly(vinylacetate) containing 0.26 molar equivalents of (-OH) functional groups dissolved in dimethyl sulfoxide. and the reaction is allowed to proceed at about llC. with agitation for about 3 hours. The resulting copolymeric product is recovered, identified as P-2. and tested as in Example I. I The results are reported in Tables H".

a .02 molar equivalent of (-OH) functional group is dissolved in a 50:50 mixture of dimethylsulfoxide and hexamethylphosphoramide. The reaction is allowed to proceed at about 130C. for 10 hours and the resulting terpolymer is recovered and identified as P-o. This compound is tested, as in Example I, and reported in Tables 1-1".

Twelve test photoreceptor strips identified respectively as T l-8 and as controls C l-4 are prepared in the usual manner by vapor condensation of a 6 p. selenium alloy (under vacuum) onto an aluminum foil substrate. A polymeric overcoat is cast onto the selenium layer from a 50:50 THF-Tetrachloroethane solution of the polymers of Examples l and ll. The test strips are then dried, and tested in the usual way for electronic properties. The control strips C l-4 are identically prepared but utilize a vinyl acetate/PVA copolymer (1:4) overcoat having a number average molecular weight of about 40,000. The results are reported in Table lll below.

TABLE lll Overcoat Surface Pf Discharge Residual Dark Decay No. Polymer a Potential (v/see'") (afier 15 sec) (v/sec") (volt.) (i= T-l P-Z 9 (+)8l0 (+)4l0 110v 30 T-2 P-2 9 (-)945 (-)350 90v 35 T-3 P-2 2l (+)l365 (+)900 l lOv T-4 P-Z 2l (H323 (-)600 lOOv 60 T-S P-3 9 (+)8l0 (+)360 100v 25 T-o P-3 9 (-)945 (--)207 l00v l4 T-7 P-Il 2l (+)l365 (+)840 80v 33 T-ll P3 2l (-')l323 (-)504 l20v 33 PVAc/PVA C-l (l:4) 9 (+)8l0 C-2 (t4) 9 ()945 (-3 (k4) 2l (+)l365 C-4 (I14) 2i (-)l323 measured at tmv/ 200 watt tungsten-iodine lamp at l5 cm "negligible discharge EXAMPLE lll (P-S) EXAMPLE VI .040 Mole of o-propyl-pyrene-l carboxaldehyde is admixed with vinylacetate/vinyl alcohol (1:10 copolymer) containing 0.04 molar equivalents of (OH) functional groups dissolved in dimethylformamide and allowed to react with agitation for 8 hours at about l20C. The resulting terpolymer product is recovered. identified as P-5. and tested as in Example I. The results are reported in Tables l-lll.

EXAMPLE lV (P-o) Example ll is repeated with .02 Mole of 6- dimethylamino-pyrene-l-carboxyaldehyde and vinylacetate/vinyl alcohol copolymer l l0) containing Six test strips identified respectively as T 9-12 and C 5-6 are prepared by applying onto an aluminized mylar substrate a photoconductive layer of about 14 p. thickness consisting of Polymer P-2 (Example l) and P-3, the control strips C 5-6 are prepared identically, but utilize the same polymer used in control C l-4 of Example V. Surface charges are applied to each sample in the usual way and the initial rate of discharge noted when continuously exposed to white light from a 200 watt Tungsteniodine lamp at a distance of 15 cm. The strips are tested as to discharge rate and flex, and reported in Table IV below.

'vg very good (no observuhle crack: or Ipllh after 3 bends over it 3" diameter pipe) g good (minor ernclu observable with it low power microscope) "ncgliguble discharge While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood that variations in form may be made thereon without departing from the spirit and scope of the invention.

What is claimed is:

l. A photoconductive member comprising a substrate and at least one organic photoconductive layer comprising an aromatic polyvinyl polymer of the formula wherein R, is defined as a hydrogen atom. a lower alkyl group or as a lower alkyl carbonyl group;

R is an aromatic polycyclic radical having 4-5 fused ring nuclei; or a 3 ringed N-containing heterocyclic group R and R are polymeric end groups;

m. n, and p are positive numbers commensurate with a number average molecular weight of at least about 5,000; m, n. and a falling within the respective ratios of about l-6z0-l 1-8 in random or block polymers.

2. A photoconductive member of claim I wherein R, is defined as hydrogen or a lower alkyl carbonyl group; and

R is a pyrene group of the formula C (lhlq (R lq wherein R and R are individually defined as a lower alkyl, a halo or a cyano group; and q is defined as 0-2;

the polymer having a number average molecular weight greater than about 5,000.

3. A photoconductive member of claim 2 wherein R is hydrogen, or a lower alkyl carbonyl group;

R is a radical of'the formulae or w (am;

and

wherein R is individually defined at each occurrence as a lower alkyl group, a halo group or a cyano group, and q is defined as 0-2; and R is a lower alkyl group, the polymer having a number average molecular weight greater than about 10,000. 4. A photoconductive member of claim 2 wherein n is defined as zero.

5. A photoconductive member of claim 3 wherein n is defined as zero.

6. A photoconductive member of claim 2 wherein 5 R, is a hydrogen atom or CH CO;

n is defined as 0 or 1; and R is defined as a radical of the formula @6 (R4)q s e A in which R, and R, are individually defined at each occurrence as hydrogen. lower alkyl, halo. or cyano groups. and q is 0-2.

7. A photoconductive member of claim 2 wherein the ratio of m:n:o is about 3-6z0-lzl-8 m, n, o and p being defined as positive integers commensurate with a molecular weight greater than about l2.000.

8. A photoconductive member of claim 7 represented by the formula wherein the number average molecular weight is greater than about 10.000.

9. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer 25 with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer represented by the for- R is defined as a hydrogen atom, a lower alkyl group or a lower alkyl carbonyl group;

R is an aromatic polycyclic radical having 4-5 fused ring nuclei; or a three-ringed N-containing heterocyclic group;

R and R are polymeric end groups;

m, n, 0 and p are positive numbers commensurate with a number average molecular weight of at least about 5,000; m, n, and 0 falling within the respective ratios of about l-6zO-l l-8 in random or block polymers.

10. A xerographic photoreceptor component comprising a substrate and at least one photoconductive 6O layer with an applied overcoat layer consisting essentially of the aromatic polyvinyl polymer of claim 9 wherein R is defined as hydrogen or a lower alkyl carbonyl group, and R is a pyrene group of the formula LII wherein R and R, are individually defined as a lower alkyl. a

halo or a cyano group; and q is defined as 0-2; the polymer having a number average molecular weight of about 5,000 to 300.000.

11. A xerographic photoreceptor component com prising a substrate and at least one photoconductiv layer with an applied overcoat layer consisting essen tially of the aromatic polyvinyl polymer of claim wherein R, is hydrogen, or a lower alkyl carbonyl group;

R, is a radical of the formulae and wherein R is individually defined at each occurrenl as a lower alkyl group. a halo group or a cyano grou and q is defined as 0-2; and R is a lower alkyl grou the polymer having a number average molecular weig greater than about l0,000.

12. A xerographic photoreceptor component cor prising a substrate and at least one photoconducti layer with an applied overcoat layer consisting csse tially of an aromatic polyvinyl polymer of claim wherein R, is a hydrogen atom or CH CO-;

n is defined as O or I; and

R is defined as a radical of the formula A c a (tide @3 "s in which R and R are individually defined at each currence as hydrogen. lower alkyl, halo, or cya groups. and q is 0-2.

13. A xerographic photoreceptor component co prising a substrate and at least one photoconduct layer with an applied overcoat layer consisting B551 tially of an aromatic polyvinyl polymer as described claim 10 wherein 3,884,689 15 the ratio of m:n:o is about 3-6:0-l:l-8; m, n, and p being defined as positive integers commensurate with a molecular weight greater than about 12,000. 14. A xerographic photoreceptor component com- 5 prising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer represented by the formula CH c H CH H/ l' fii' 2 CH/ 2 greater than about 10,000.

1 i t I t 

1. A PHOTOCONDUCTIVE MEMBER COMPRISING A SUBSTRATE AND AT LEAST ONE ORGANIC PHOTOCONDUCTIVE LAYER COMPRISING AN AROMATIC POLYVINYL POLYMER OF THE FORMULA
 2. A photoconductive member of claim 1 wherein R1 is defined as hydrogen or a lower alkyl carbonyl group; and R2 is a pyrene group of the formula
 3. A photoconductive member of claim 2 wherein R1 is hydrogen, or a lower alkyl carbonyl group; R2 is a radical of the formulae
 4. A photoconductive member of claim 2 wherein n is defined as zero.
 5. A photoconductive member of claim 3 wherein n is defined as zero.
 6. A photoconductive member of claim 2 wherein R1 is a hydrogen atom or CH3CO-; n is defined as 0 or 1; and R2 is defined as a radical of the formula
 7. A photoconductive member of claim 2 wherein the ratio of m: n:o is about 3-6:0-1:1-8 m, n, o and p being defined as positive integers commensurate with a molecular weight greater than about 12,000.
 8. A photoconductive member of claim 7 represented by the formula
 9. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer represented by the formula
 10. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the aromatic polyvinyl polymer of claim 9 wherein R1 is defined as hydrogen or a lower alkyl carbonyl group; and R2 is a pyrene group of the formula
 11. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the aromatic polyvinyl polymer of claim 9 wherein R1 is hydrogen, or a lower alkyl carbonyl group; R2 is a radical of the formulae
 12. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer of claim 9 wherein R1 is a hydrogen atom or CH3CO-; n is defined as 0 or 1; and R2 is defined as a radical of the formula
 13. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer as described in claim 10 wherein the ratio of m:n:o is about 3-6:0-1:1-8; m, n, o and p being defined as positive integers commensurate with a molecular weight greater than about 12,000.
 14. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of an aromatic polyvinyl polymer represented by the formula 